This disclosure relates in general to bulk material bins, and more particularly, to a mass flow bulk material bin.
Typically, a hopper bottom bin for flowable bulk materials, such as, dry powders or toner used in copiers/printers has a vertical cylindrical section joined at its lower edge to a conical or frusta-conical hopper. The bin is filled through an inlet opening at the top of the cylindrical section, and is emptied through an outlet at the lowermost point of the hopper. Discharge apparatus for guiding the material from the bin to its destination or starting and stopping the discharge flow is commonly bolted or welded to a bolt ring mounted around the outer surface of the hopper at its bottom.
While the heretofore-mentioned configurations are typical, the geometry of bins varies. For example, the inlet opening may be centered over the bin, or positioned to one side of the bin roof or on a sidewall of the bin. The hopper may be a right circular cone with a centered outlet, or a cone having an oblique axis and an outlet that does not lie along the central axis of the bin.
In nearly all bins, despite these variations, the segregation of material according to particle size, shape or density as it is introduced into a bin creates a problem. Material deposited in a bin generally forms a conical pile centered under the inlet opening, with coarse particles tending to roll outward down to the periphery of the bin and fine particles tending to accumulate in the center. This results in segregation of different size particles in different regions with the bin.
Yet another problem common to many bins is a tendency for segregation of material to become enhanced as the material is discharged from the bin. This is a result of funnel flow, where material directly above the discharge outlet moves downward at a greater speed than material elsewhere, while material in some regions of the bin may not move at all. If the outlet is located directly under the inlet, the fine particles that tend to accumulate directly under the inlet will be discharged before the coarser one, resulting in more pronounced segregation. If the outlet is elsewhere, the coarser particles will be discharged first, and more pronounced segregation will still result.
Another undesirable effect of funnel flow is that it causes layers of material deposited at successive time intervals to intermix in an uncontrolled manner. In some circumstances it is desirable to have material exit a bin in the same order that it entered, while in other situations, it may be desirable for material from successive layers to be blended together as the bin is emptied. Adequate control of the extent of the intermixing of layers, either to prevent or to promote their blending, is not provided by the structure of most bins.
In contrast to funnel flow, where some material in a bin moves downward while a portion remains stationary, mass flow is a condition where all material in the bin moves simultaneously, and not stand still. But, mass flow is difficult to obtain because the vast majority of bins are shaped like funnels, i.e., cylindrical vessels with a converging lower part that helps to contain and direct the discharge. The inherent exit flow problems of all symmetrically shaped bins filled with powder materials are bridging and “rat-holing”. Bridging is when the powder forms internal spherical structure (arches), thus restricting of completely blocking the flow. “Rat-hole” effect is when, due to the different friction forces between, for example, toner particles and other toner particles and toner particles and bin walls, a hole is formed in the toner mass at the bin's exit. This hole is also shaped like a funnel and remains constantly open. Thus, when a batch of new, highly fluidized toner is dumped into the bin, it travels directly through the “rat-hole” since it does not have time to settle. Therefore, when a valve in the bin's hopper is opened, the highly fluidized freshly dumped toner uncontrollably flows through the “rat-hole” flooding the hopper. To prevent bridging and “rat-holing,” relatively small hoppers are equipped with a rotating agitator in the form of a mechanical arm. This solution for a bin of 1000 kg would be extremely difficult and would require big energy consuming motor and gearbox. Smaller devices like fluidizers (air injectors) or small agitators positioned near the exit are not always effective or change the density of the material in a harmful way.
Other attempts at improving the flow of controlling the flow of powders include U.S. Pat. No. 5,517,595 issued Apr. 8, 1997 to Jerry R. Johnson et al. employs a cylindrical bin and a conical transition section disposed below the cylindrical bin. In one embodiment, a baffle having triangular cross-sectional areas is disposed within the conical transition section. In another embodiment, the transition section is formed with triangular-shaped, flat side outer panels.
A blending apparatus is disclosed in U.S. Pat. No. 4,286,883 to Johanson includes a conical insert to promote mass flow movement of material in a self-emptying hopper.
Solid particulate material is moved through a hopper bottom bin shown in U.S. Pat. No. 4,548,342 issued Oct. 22, 1985 to Glen W. Fisher in mass flow inducted by a conical surface positioned within the hopper to compensate for the shallowness thereof. Laminar mass flow movement will occur in the uppermost region of the material within the vertical bin walls. The hopper cross-section is separated into segregated flow channels by the conical surface, and by webs extending therefrom. The conical surface and webs have overall dimensions small enough for insertion through a bolt ring on the bottom of the hopper. The proportions of the material flowing through each channel is chosen to achieve a desired discharge flow pattern by varying the relative cross-sectional areas of either the inlets or the outlets of the channels. This results in changes in the velocity profile of the downwardly flowing material in a zone above and adjacent to the separate flow channels.
U.S. Pat. No. 5,769,281 issued Jun. 23, 1998 to Lyndon Bates discloses an insert system for changing the pattern of material flow in a bulk storage hopper during the discharge process, from a form where a channel flow develops within a mass of static material into a form where the entire stored contents are caused to flow. This change is affected by the provision of insert members supported within the hopper, which modify the stress pattern in the flowing contents to allow the bulk material to deform more readily and for slip to take place on all contact surfaces between the material and the hopper walls.
U.S. Pat. Nos. 6,328,183 B1 issued Dec. 11, 2001 to Clarence B. Coleman discloses a bin for storing dry powder bulk material or granules. Bulk material is deposited in an upper section of the bin and is discharged from the bottom of the lower section of the bin. The lower section of the bin is formed with oppositely directed, downwardly sloping walls, joined by opposing vertical walls. The downwardly sloping walls, respectively, slope downwardly at an angle greater than the angle of repose of the material or granules in the bin. Disposed in the lower section of the bin is a planar vertical divider wall that is supported by the vertical walls of the lower section. The vertical divider wall has flat surfaces that face, respectively, the oppositely directed, downwardly sloping walls of the lower section for reducing bridging of the dry powder bulk material or granules in the bulk material bin during mass flow from the upper section through the lower section of the bin.
Thus, the bulk materials handling art has long needed a system that can achieve or exceed the flow control provided by prior art devices, while being easily retrofitted to a variety of existing hopper bottom bins. Especially, if such a device would be inexpensive to manufacture and ship, and would be installed with little or no on-site alteration of preexisting bin structure.
Accordingly, a bin partition that improves flow of powder or particulate material is disclosed that is to be installed into an existing bin. The partition has a triangular-like cross-section with a baffle on top thereof covering a portion of the partition. The partition changes the shape of the exit area of a bin and enables better control of powder or particulate material flow, thus preventing bridging and uncontrolled flooding while filling a bin's hopper.
While the disclosure will be described hereinafter in connection with a preferred embodiment thereof, it will be understood that limiting the disclosure to that embodiment is not intended. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.